This invention relates to a motor protector for oil-filled submersible electric motors and, more particularly, to a motor protector having a prolonged operational life and increased resistance to chemical attack.
A variety of fluids is pumped from subterranean zones with a variety of different types of pumps. In the production of petroleum, it is common to employ electric submersible systems for lifting the fluids collected in the well. Such systems generally include a submersible pump and a submersible oil-filled electric motor separated by a seal or protector assembly. The seal or protector functions, in part, to provide a reservoir of motor fluid in communication with the electric motor, to allow for thermal expansion and contraction of the motor fluid, and to keep the well fluid out of the motor. Well fluid generally comprises salt water, particulate solids and other contaminants that are deleterious to the motor.
There are two types of motor protectors commonly used in the field. One type is referred to as a bladder or bag protector. The bladder, positioned within the protector assembly housing, provides a positive barrier between the well fluid outside the bladder and the motor fluid within. It is made of an elastomeric material that flexes to provide a variable capacity chamber thus accommodating volume changes in the motor oil. Generally, a vent through the housing is utilized to allow entry and expulsion of well fluid between the housing interior and the well bore as required by the expansion and contraction of the elastomeric bladder.
The other common type of motor protector is normally referred to as a “labyrinth” type protector. The labyrinth design uses a series of cavities and vertical labyrinth paths to keep the well fluid and the motor fluid separated. The two fluids are in direct contact; therefore, the effectiveness of the device depends on the difference in specific gravity and the immiscibility between the well fluid and the motor fluid. The design allows for expansion and contraction of the motor fluid by providing a vent through the housing wherethrough well fluid can enter or be withdrawn from the adjacent cavity in response to changes in motor fluid volume.
The motor protectors are often used in combination. For example, one or more labyrinth-type protectors may be used above or below one or more bladder protectors. Usually, motor fluid in the bladder communicates directly with a passage to the motor. Therefore, a failure of the elastomeric material comprising the bladder creates a short path for well fluid subsequently penetrating the bladder to reach the motor.
The bladder is usually made of a high-temperature, high-performance elastomer that is resistant to the harsh conditions encountered downhole. However, there is still a need to reduce the chemical attack of well fluid contaminants or impurities on the elastomer and thus prolong the operational life of the bladder elastomer itself and ultimately the motor protector and submersible motor assembly.